As processing capabilities increase, mobile computing devices demand more performance and additional features. In turn, the power requirements for these mobile computing devices may increase. For example, thermal design power (TDP) for notebook platforms could reach about 80 W in the near future. The increased power requirements, in conjunction with compact platform designs, place a huge burden on the power delivery design internal to the battery pack.
Battery packs are subject to several design constraints. As the package size of electronic devices decreases, the size of battery packs may be limited. Similarly, the size of battery packs may be limited as the amount of electronics within a device increases. Also, the heat produced and dissipated by a battery pack may constrain battery pack design with respect to specified operating levels. One common source of heat within battery packs are resistive sensor elements used to measure the operating current drawn from or to the battery. Additionally, battery packs may be designed to accommodate various operating power states, depending on the operating conditions of the corresponding electronic device.
Battery pack designs are also subject to power management requirements. Many battery packs incorporate power management electronics to determine power usage. Such electronics also typically estimate how much power and operating time or both are available for continued use of the corresponding device. For example, notebook computer platforms generally notify a user of the amount of time the user may continue to use battery power to operate the notebook. This estimation is often referred to as “gas gauging” or “fuel gauging” as an analogy to the use of fuel gauges in automobiles to indicate the amount of fuel in the tank at a given time. Unfortunately, gas gauging in computing platforms is subject to errors that are not necessarily a problem in automobile fuel tanks which use mechanical floats. As electrical energy is depleted from the battery pack, the estimation of remaining operating time may be subject to inaccuracies due to the monitoring range of the power management electronics. Where little power is used such as in a low-power operating state, the inaccuracy of the estimation may be significant because the monitoring range of the power management electronics is typically static and is not calibrated to monitor low-power states.
Conventional technology for battery packs does not adequately address these design constraints. In particular, conventional battery packs suffer from significant heat generation from using series resistive elements to measure operating currents. Also, conventional battery packs suffer from inaccurate power management because of the use of static monitoring ranges.